The study of formation process of colloidal silica

Two formation processes of colloidal silica were discussed, one is the constant volume process and the other is the constant concentration process. In the constant volume process, the reaction volume is kept constant during titrating active silicic acid. The adding volume of active silicic acid is equal to the evaporative volume of heating solution, therefore, the total volume of heating solution is fixed during titrating. On the other hand, the constant concentration process is essentially a reflux process so the volume of heating reaction is accumulated. According to the experimental results, the colloidal silica formed by the constant volume has the larger particle size than that formed by the constant concentration process. The variation of the particle number and the particle concentration during titration was calculated according to the particle size data from DLS measurement.